Bicomponent spunbond nonwoven web

ABSTRACT

Disclosed are nonwoven webs comprising a plurality of continuous spunbonded bicomponent fibers, wherein each of the plurality of bicomponent fibers comprises 75% by weight of poly(ethylene terephthalate) in a core and 25% by weight of poly(trimethylene terephthalate) in a sheath surrounding the core, wherein the amounts in % by weight are based on the total weight of the bicomponent fiber.

FIELD OF THE INVENTION

The present invention relates to bicomponent spunbond nonwoven webshaving improved strength.

TECHNICAL BACKGROUND

Nonwoven webs are well known in the art and can be formed using anysuitable technique, such as, flash spinning, spunbonding, meltblowing,and hydro-entanglement. Each of these techniques produces nonwoven webswith certain characteristics useful for a particular application. Forexample, nonwoven webs formed by meltblowing are more breathable, butare not as strong as those formed by spunbonding. Nonwoven webs formedusing bicomponent fibers can further provide additional benefits.

US 20020127939 to Hwo et al. disclose a bicomponent meltblown microfibernonwoven material wherein at least two different polymers includingpolytrimethylene terephthalate have been extruded, spun together, andthen meltblown.

US 20030124941 to Hwo et al. disclose spunbonded nonwoven materials madefrom polytrimethylene terephthalate having a hydrostatic head of lessthan 10 cm.

There is an ongoing search for new compositions and techniques that canresult in low cost, environmentally sustainable, nonwoven webs havingsuperior mechanical properties.

SUMMARY

In an aspect of the invention, there is a nonwoven web comprising aplurality of continuous spunbond fibers, wherein each of the pluralityof continuous spunbond fibers comprises:

-   -   a) 75%, by weight of poly(ethylene terephthalate) in a core; and    -   b) 25%, by weight of poly(trimethylene terephthalate) in a        sheath surrounding the core,    -   wherein the amounts in % by weight are based on the total weight        of the continuous spunbonded fiber.

In another aspect, there is a nonwoven web comprising a plurality ofcontinuous spunbond fibers, wherein each of the plurality of continuousspunbond fibers comprises:

-   -   a) 50%, by weight of poly(ethylene terephthalate) in a core; and    -   b) 50%, by weight of poly(trimethylene terephthalate) in a        sheath surrounding the core,    -   wherein the amounts in % by weight are based on the total weight        of the continuous spunbonded fiber.

DETAILED DESCRIPTION

Disclosed is a nonwoven web comprising a plurality of continuousspunbonded fibers, wherein each of the plurality of continuous spunbondfibers comprises poly(ethylene terephthalate) (PET) in a core andpoly(trimethylene terephthalate) (PTT) in a sheath surrounding the core.

As used herein, the term “nonwoven web” is used interchangeably with“nonwoven sheet”, “nonwoven layer” and “nonwoven fabric”. As usedherein, the term “nonwoven” means a manufactured sheet, web or batt ofrandomly orientated fibers, filaments, or threads positioned to form aplanar material without an identifiable pattern. Examples of nonwovenwebs include meltblown webs, spunbond webs, carded webs, air-laid webs,wet-laid webs, and spunlaced webs and composite webs comprising morethan one nonwoven layer. Nonwoven webs for the processes and articlesdisclosed herein are desirably prepared using a “direct laydown”process. “Direct laydown” means spinning and collecting individualfibers or plexifilaments directly into a web or sheet without windingfilaments on a package or collecting a tow.

The term “spunbond fibers” as used herein means fibers that are formedby extruding molten thermoplastic polymer material as fibers from aplurality of fine, usually circular, capillaries of a spinneret with thediameter of the extruded fibers then being rapidly reduced by drawingand then quenching the fibers. Other fiber cross-sectional shapes suchas oval, multi-lobal, etc. can also be used. Spunbond fibers aregenerally continuous and usually have an average diameter of greaterthan about 5 micrometers. Spunbond nonwoven webs are formed by layingfibers randomly on a collecting surface such as a foraminous screen orbelt and spunbonding the fibers by methods known in the art such as byhot-roll calendering or by passing the web through a saturated-steamchamber at an elevated pressure. For example, the nonwoven web can bethermally point bonded at a plurality of thermal bond points locatedacross the nonwoven web.

As used herein, the term “bicomponent fiber” refers to a fibercomprising a pair of polymer compositions intimately adhered to eachother along the length of the fiber, so that the fiber cross-section is,for example, a side-by-side, sheath-core or other suitablecross-section. The bicomponent sheath/core polymeric fibers can beround, trilobal, pentalobal, octalobal, like a Christmas tree,dumbbell-shaped, island-in-the-sea or otherwise star shaped in crosssection. The fibers may also be in a side by side arrangement.

As used herein, the term “continuous fiber” refers to a fiber ofindefinite or extreme length. In practice, there could be one or morebreaks in the “continuous fiber” due to manufacturing process, but a“continuous fiber” is distinguishable from a staple fiber which is cutto a predetermined length.

The nonwoven web disclosed herein comprises a plurality of continuousspunbonded bicomponent fibers in a sheath-core configuration. The weightratio between the sheath component and the core component of thedisclosed spunbonded bicomponent fibers is preferably 25:75. Thebicomponent fibers have an average fiber diameter in the range of 2microns to 20 microns. In an embodiment, each bicomponent fibercomprises 75%, by weight of PET in the core and 25%, by weight of PTT inthe sheath surrounding the core. Yet, in another embodiment, eachbicomponent fiber comprises 50%, by weight of PET in the core and 50%,by weight of PTT in the sheath surrounding the core.

The PTT used in the sheath component of the spunbond fibers of thedisclosed nonwoven web has an intrinsic viscosity in the range of 0.9dl/g to 1.3 dl/g or 0.95 dl/g to 1.05 dl/g.

In an embodiment, “poly(trimethylene terephthalate)” (PTT) is ahomopolymer or a copolymer comprising at least 70 mole percenttrimethylene terephthalate repeating units. The preferredpoly(trimethylene terephthalate)s contain at least 85 mole percent, morepreferably at least 90 mole percent, even more preferably at least 95 orat least 98 mole percent, and most preferably about 100 mole percent,trimethylene terephthalate repeating units.

Examples of copolymers include copolyesters made using 3 or morereactants, each having two ester forming groups. For example, acopoly(trimethylene terephthalate) can be made using a comonomerselected from the group consisting of linear, cyclic, and branchedaliphatic dicarboxylic acids having 4-12 carbon atoms (for examplebutanedioic acid, pentanedioic acid, hexanedioic acid, dodecanedioicacid, and 1,4-cyclo-hexanedicarboxylic acid); aromatic dicarboxylicacids other than terephthalic acid and having 8-12 carbon atoms (forexample isophthalic acid and 2,6-naphthalenedicarboxylic acid); linear,cyclic, and branched aliphatic diols having 2-8 carbon atoms (other than1,3-propanediol, for example, ethanediol, 1,2-propanediol,1,4-butanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol,2-methyl-1,3-propanediol, and 1,4-cyclohexanediol). The comonomertypically is present in the copolyester at a level in the range of about0.5 to about 15 mole percent, and can be present in amounts up to 30mole percent.

In a preferred embodiment, PTT is made by polycondensation of1,3-propanediol derived from a renewable source and terephthalic acid oracid equivalent. In an embodiment, the PTT contains at least 20%renewably sourced ingredient by weight and in some cases at least 30%.An exemplary PTT suitable for the disclosed nonwoven web is availablefrom DuPont Company (Wilmington, Del.) under the trademark Sorona®. Inan embodiment, the disclosed nonwoven webs have renewably sourcedcontent of at least 5% by total weight of the web.

The renewably sourced 1,3-propanediol contains carbon from theatmospheric carbon dioxide incorporated by plants, which compose thefeedstock for the production of the 1,3-propanediol. In other words, therenewably sourced 1,3-propanediol contains only renewable carbon, andnot fossil fuel-based or petroleum-based carbon.

A particularly preferred renewable source of 1,3-propanediol is via afermentation process using a renewable biological source such as cornfeed stock. For example, bacterial strains able to convert glycerol into1,3-propanediol are found in the species Klebsiella, Citrobacter,Clostridium, and Lactobacillus. The technique is disclosed in severalpublications, including U.S. Pat. Nos. 5,633,362, 5,686,276 and5,821,092. U.S. Pat. No. 5,821,092 discloses, inter alia, a process forthe biological production of 1,3-propanediol from glycerol usingrecombinant organisms. The process incorporates E. coli bacteria,transformed with a heterologous pdu diol dehydratase gene, havingspecificity for 1,2-propanediol. The transformed E. coli is grown in thepresence of glycerol as a carbon source and 1,3-propanediol is isolatedfrom the growth media. Since both bacteria and yeasts can convertglucose (e.g., corn sugar) or other carbohydrates to glycerol, theprocesses disclosed in these publications provide a renewable source of1,3 propanediol monomer.

Therefore, PTT derived from the renewably sourced 1,3-propanediol hasless impact on the environment as the 1,3 propanediol used in thecompositions does not deplete diminishing fossil fuels and, upondegradation, releases carbon back to the atmosphere for use by plantsonce again. Thus, the compositions of the present invention can becharacterized as more natural and having less environmental impact thansimilar compositions comprising petroleum based 1,3 propanediol.

Poly(ethylene terephthalate) (PET) can include a variety of comonomers,including diethylene glycol, cyclohexanedimethanol, poly(ethyleneglycol), glutaric acid, azelaic acid, sebacic acid, isophthalic acid,and the like. In addition to these comonomers, branching agents liketrimesic acid, pyromellitic acid, trimethylolpropane andtrimethyloloethane, and pentaerythritol may be used. The poly(ethyleneterephthalate) can be obtained by known polymerization techniques fromeither terephthalic acid or its lower alkyl esters (e.g. dimethylterephthalate) and ethylene glycol or blends or mixtures of these. ThePET used in the core component of the spunbond fibers of the disclosednonwoven web has an intrinsic viscosity in the range of 0.58 dl/g to0.75 dl/g or 0.62 dl/g to 0.69 dl/g.

The sheath and/or core component of the sheath-core spunbond fibers caninclude other conventional additives such as dyes, pigments,antioxidants, ultraviolet stabilizers, spin finishes, and the like. Inan embodiment, the sheath comprises 0.1% to 0.33%, by weight of titaniumdioxide dispersed in the PTT. The titanium dioxide having an averageparticle size of about 300 nm.

The nonwoven web disclosed hereinabove can be prepared using spunbondingmethods known in the art, for example as described in Rudisill, et al.U.S. Patent application Ser. No. 60/146,896 filed on Aug. 2, 1999, whichis hereby incorporated by reference (published as PCT Application WO01/09425). The spunbonding process can be performed using eitherpre-coalescent dies, wherein the distinct polymeric components arecontacted prior to extrusion from the extrusion orifice, orpost-coalescent dies, in which the distinct polymeric components areextruded through separate extrusion orifices and are contacted afterexiting the capillaries to form the bicomponent fibers.

The disclosed nonwoven web can be made using any suitable bicomponentspinning system, for example Model # NF5, manufactured by Nordson FiberSystems Inc. (Duluth, Ga.) and Hills Inc. (W. Melbourne, Fla.). First,the two polymers PET and PTT are dried at a temperature in the range of90° C. to 120° C. to a moisture content of less than 50 ppm. Afterdrying, the two polymers are separately extruded at a temperature abovetheir melting point and below the lowest decomposition temperature. PTTcan be extruded at 245° C. to 265° C. and PET at 280° C. to 295° C.After extrusion, the two polymer are metered to a spin-pack assembly,where the two melt streams are separately filtered and then combinedthrough a stack of distribution plates to provide multiple rows ofsheath-core fiber cross-sections. The spin-pack assembly is kept at 285°C. to 295° C. The PTT and PET polymers can be spun through the eachcapillary at a polymer throughput rate of 0.5 g/hole/min to 3g/hole/min. An attenuating force using rectangular slot jet can beapplied to the bundle of fibers. The bicomponent fibers exiting the jetare collected on a forming belt to form a nonwoven web of bicomponentfibers. Vacuum can be applied underneath the belt to help pin thenonwoven web to the belt. The speed of the belt can be varied to obtainnonwoven webs of various basis weights.

The nonwoven web can be thermally bonded using methods known in the art.In one embodiment, the nonwoven web is thermally bonded with adiscontinuous pattern of points, lines, or other pattern of intermittentbonds using methods known in the art. Intermittent thermal bonds can beformed by applying heat and pressure at discrete spots on the surface ofthe spunbond web, for example by passing the layered structure through anip formed by a patterned calender roll and a smooth roll, or betweentwo patterned rolls. One or both of the rolls are heated to thermallybond the web. When web breathability is important, such as in garmentend uses, the webs are preferably bonded intermittently to provide amore breathable web.

In one method, the nonwoven web is thermally bonded in a nip formedbetween two smooth metal rolls at bonding temperature in the range of110° C. to 130° C. and a bonding nip pressure in the range of 500 N/cmto 1500 N/cm. The optimum bonding temperature and pressure are functionsof the line speed during bonding, with faster line speeds generallyrequiring higher bonding temperatures. The thermally bonded sheet wasthen wound onto a roll.

During thermal pattern bonding, the PTT in the sheath component of thespunbond fibers is partially melted in the discrete areas correspondingto raised protuberances on the patterned roll to form fusion bonds thatbond the spunbond fibers together to form a cohesively bonded spunbondsheet. Depending on the bonding conditions and polymers used in thesheath component, the polyethylene in the sheath component may also bepartially melted during thermal pattern bonding. The PET core componentis not melted during thermal bonding and contributes to the strength ofthe web. The bonding roll pattern may be any of those known in the art,and preferably is a pattern of discrete point or line bonds. Thenonwoven web can also be thermally bonded using ultrasonic energy, forexample by passing the web between a horn and a rotating anvil roll, forexample an anvil roll having a pattern of protrusions on the surfacethereof.

Alternately, the nonwoven web can be bonded using through-air bondingmethods known in the art, wherein heated gas such as air is passedthrough the web at a temperature sufficient to bond the fibers togetherwhere they contact each other at their cross-over points while the webis supported on a porous surface.

The disclosed spunbonded nonwoven web comprising PTT-PET as sheath-corefibers have surprisingly higher strength (tensile strength, grab tearstrength, and Mullen burst) than a comparable spunbonded nonwoven web ofPET-PTT as sheath-core fibers or 100% PTT fibers or 100% PET fibers. Thedisclosed nonwoven webs have a basis weight in the range of 25 gsm to500 gsm or 40 gsm to 200 gsm or 50 gsm to 150 gsm. As used herein, theterm “machine direction” (MD) refers to the direction in which anonwoven web is produced (e.g. the direction of travel of the supportingsurface upon which the fibers are laid down during formation of thenonwoven web). The term “cross direction” (XD) refers to the directiongenerally perpendicular to the machine direction in the plane of theweb.

The disclosed nonwoven webs have a tensile strength per unit basisweight in the range of 0.7 N/gsm to 5 N/gsm or 0.75 N/gsm to 2 N/gsm,measured in both the machine direction and the cross-direction of theweb (according to ASTM D1117-01 and D5035-95).

In another embodiment, the disclosed nonwoven webs have a grab tearstrength per unit basis weight in the range of 1.5 N/gsm to 10 N/gsm or1.5 N/gsm to 5 N/gsm, measured in both the machine direction and thecross-direction of the web (according to ASTM D1117-01

In another embodiment, the disclosed nonwoven webs have a Mullen burstper unit basis weight in the range of 3.5 KPa/gsm to 10 KPa/gsm or 3.5KPa/gsm to 5 KPa/gsm, measured in both the machine direction and thecross-direction of the web.

In an embodiment, the disclosed nonwoven webs have a trapezoidal tearstrength per unit basis weight in the range of 0.4 N/gsm to 5 N/gsm or0.4 N/gsm to 0.75 N/gsm, measured in both the machine direction and thecross-direction of the web (according to ASTM 5733).

The disclosed spunbonded nonwoven webs can be used in a broad range ofapplications such as, protective apparel, hot gas filtration, and laserprintable substrate.

In an embodiment, there is an article comprising the disclosed nonwovenwebs. In some embodiment, the article is a protective apparel. In otherembodiment, the article is a filter for hot gas filtration. In anotherembodiment, the article is a laser printable media comprising thedisclosed nonwoven webs as a substrate.

As used herein, the phrase “one or more” is intended to cover anon-exclusive inclusion. For example, one or more of A, B, and C impliesany one of the following: A alone, B alone, C alone, a combination of Aand B, a combination of B and C, a combination of A and C, or acombination of A, B, and C.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of embodiments of the disclosed compositions,suitable methods and materials are described below.

In the foregoing specification, the concepts have been disclosed withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the invention as set forth in theclaims below.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all embodiments.

It is to be appreciated that certain features are, for clarity,described herein in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.Further, reference to values stated in ranges includes each and everyvalue within that range.

The concepts disclosed herein will be further described in the followingexamples, which do not limit the scope of the invention described in theclaims.

The examples cited here relate to spunbonded nonwoven web. Thediscussion below describes how a spunbonded nonwoven web comprising aplurality of bicomponent fibers can be formed, and tested for strengthproperties.

Unless specified otherwise, compositions are given as weight percents.

EXAMPLES Preparation of Bicomponent Spunbond Nonwoven Webs

Nonwoven web comprising bicomponent fibers was made from a poly(ethyleneterephthalate) (PET) component and a poly(trimethylene terephthalate)(PTT) component. The PET component was obtained from Dupont Company (OldHickory, Tenn.) as PET resin grade 4434 and had an intrinsic viscosity(IV) of 0.67 dl/g. The PTT component, D13454709 Sorona® J2241 semi-dullis also available from Dupont Company (Wilmington, Del.). The PTT usedhad an IV of 1.02 dl/g; Mn˜28000; and about 37% renewably sourcedingredients by weight

Both the PET resin and the PTT resin were dried in a through air dryerat a temperature of 100° C. to a moisture content of less than 50 ppm.

A bicomponent spinning system, Model # NF5, manufactured by NordsonFiber Systems Inc. (Duluth, Ga.) and Hills Inc. (W. Melbourne, Fla.) wasused for creating the spunbond structures. The two components wereseparately extruded and metered to a spin-pack assembly, where the twomelt streams were separately filtered and then combined through a stackof distribution plates to provide multiple rows of sheath-core fibercross-sections. The spin-pack assembly consisted of a total of 1162round capillary openings. The width of the forming zone was 56 cm. Thespin-pack assembly was heated to 295° C. The PTT and PET polymers werespun through the each capillary at a polymer throughput rate of 1.0g/hole/min.

The bundle of fibers were cooled in a cross-flow quench extending over alength of 75 cm. An attenuating force was provided to the bundle offibers by a rectangular slot jet. The distance between the spin-pack tothe entrance to the jet was 63 cm.

The fibers exiting the jet were collected on a forming belt. Vacuum wasapplied underneath the belt to help pin the fibers to the belt. Thefibers were then thermally bonded in a nip formed between two smoothmetal rolls, both rolls being heated to 155° C., with a nip pressure of714 N/cm. The thermally bonded sheet was then wound onto a roll.

The speed of the belt was varied to obtain spunbonds of various basisweights. The belt speed was set at 42 m/min to obtain 50 gsm spunbond.It was slowed down to 21 m/min to obtain 100 gsm sheet and was furtherslowed to 14 m/min to obtain 150 gsm sheet.

Basis Weight is a measure of the mass per unit area of a web or sheetand was determined by ASTM C-3776, which is hereby incorporated byreference, and is reported in g/m², abbreviated as gsm.

Table 1 summarizes the exemplary bicomponent spunbonds composition andbasis weight. The sheath and the core comprise one polymeric componenteach, either PTT or PET. Hence, in Example 2, 25 weight % PTT in thesheath and 75 weight % PET in the core means that the sheath comprisespure PTT and the core comprises pure PET, such that the weight ratio ofsheath to core is 25:75.

In Examples 1 and 2, the core of the bicomponent spunbonds comprised PETcomponent and the sheath comprised PTT component. Whereas, in theComparative Examples B and C, summarized in Table 2, the core comprisedPTT component and the sheath comprised PET component. The ComparativeExample A was 100% PET spunbond with both the sheath and the corecomprising PET. The Comparative Example D was 100% PTT spunbond withboth the sheath and core comprising PTT.

TABLE 1 Composition of Exemplary Bicomponent Spunbond Web Composition(weight % based on the total Basis weight of the fiber) weight Example #Sheath Core (gsm) 1 1-1 50% PTT 50% PET 50 1-2 50% PTT 50% PET 100 1-350% PTT 50% PET 150 2 2-1 25% PTT 75% PET 50 2-2 25% PTT 75% PET 100 2-325% PTT 75% PET 150

TABLE 2 Comparative Bicomponent spunbonds Composition (weight % based onthe total Basis Comparative weight of the fiber) weight Example # SheathCore (gsm) A A-1 100% PET 100% PET 50 A-2 100% PET 100% PET 100 A-3 100%PET 100% PET 150 B B-1  50% PET  50% PTT 50 B-2  50% PET  50% PTT 100B-3  50% PET  50% PTT 150 C C-1  25% PET  75% PTT 50 C-2  25% PET  75%PTT 100 C-3  25% PET  75% PTT 150 D D-1 100% PTT 100% PTT 50 D-2 100%PTT 100% PTT 100 D-3 100% PTT 100% PTT 150

Measurement of Nonwoven Web Strength and Wear

The spunbond nonwoven webs (1, 2, A, B, C, and D), prepared supra, weretested for strength (Grab tear, Trapezoidal tear, Strip tensile andMullen burst) using the following standard ASTM (American Society forTesting and Materials) methods for nonwovens as follows:

Strip Tensile strength is a measure of the breaking strength of a sheetand was conducted on a 2.54-cm (1-inch) wide strip according to ASTMD1117-01, D5035-95, and is reported in Table 5.

TABLE 3 Strip Tensile Strength of Exemplary and Comparative BicomponentSpunbond Webs Strip Tensile, MD Strip Tensile, XD Load/ Load/ Basisbasis basis weight Sample Load Strain weight Load Strain weight (gsm) #(N) (%) (N/gsm) (N) (%) (N/gsm) 50 A-1 24.72 11.12 0.4944 11.6 22.730.2320 B-1 29.59 11.61 0.5918 17.44 30.61 0.3488 C-1 29.91 7.03 0.598218.26 32.45 0.3652 D-1 26.02 7.27 0.5204 17.68 21.94 0.3536 1-1 54.4750.23 1.0894 51.21 57.95 1.0242 1-2 64.17 58.24 1.2834 43.69 52.620.8738 100 A-2 40.59 8.98 0.4059 25.95 10.21 0.2595 B-2 43.86 5.2 0.438638.16 14.36 0.3816 C-2 41.87 5.08 0.4187 44.52 15.64 0.4452 D-2 37.225.74 0.3722 41.93 17.36 0.4193 2-1 90.94 36.6 0.9094 81.7 54.77 0.81702-2 133.99 59.89 1.3399 125.05 77 1.2505 150 A-3 66.45 8.49 0.4430 40.995.44 0.2733 B-3 51.81 6.66 0.3454 45.17 10.08 0.3011 C-3 58.18 60.320.3879 63.71 13.69 0.4247 D-3 44.95 5.62 0.2997 57.42 10.7 0.3828 3-1174.94 52.44 1.1663 168.89 73.52 1.1259 3-1 257.75 85.31 1.7183 205.8882.68 1.3725

Table 3 suggests that at a given basis weight, the spunbond webs withPTT in the sheath (Examples 1 and 2) exhibit substantially highertensile strength both in the machine direction and the cross directionas compared to the spunbond webs with PTT in the core (ComparativeExamples B and C); 100% pure PTT spunbond web (Comparative Example D);and 100% pure PET spunbond web (Comparative Example A). Furthermore, at100 gsm and 150 gsm, the spunbond webs containing 25 weight % PTT in thesheath (Examples 2-2 and 2-3) are stronger than those containing 50weight % PTT in the sheath (Examples 1-2 and 1-3).

Mullen burst test measures the pressure required to burst a web and wasconducted according to ASTM D1117-01, D5035-95 and is reported in unitsof force per unit area KPa.

TABLE 4 Mullen burst test results of Exemplary and ComparativeBicomponent Spunbond Webs Mullen burst/basis [Basis weight Sample Mullenburst weight (gsm) # (KPa) (KPa/gsm) 50 A-1 148.93 2.9786 B-1 99.291.9858 C-1 100.67 2.0134 D-1 91.01 1.8202  1-1 267.53 5.3506  2-1 260.635.2126 100 A-2 319.93 3.1993 B-2 157.21 1.5721 C-2 153.07 1.5307 D-2154.45 1.5445  1-2 479.89 4.7989  2-2 619.17 6.1917 150 A-3 >827.4 — B-3315.791 2.1053 C-3 199.955 1.3330 D-3 244.083 1.6272  1-3 714.322 4.7621 2-3 >827.4 —

Table 4 shows that at 100 and 150 gsm, the spunbond webs with PTT in thesheath (Examples 1 and 2) have higher Mullen burst pressures than thecomparative examples with PTT in the core (Comparative Examples B andC). At 150 gsm, the Mullen burst of Example 2-3 (PTT in the sheath) andcomparative Example A-3 (100% PET) could not be measured as they werebeyond the instrument limit. However, it is clear that Example 1-3 isstronger than Comparative Examples B-3 (50% PET in the sheath), C-3 (25%PET in the sheath) and D-3 (100% PTT).

Grab tear strength, is a measure of force required to tear a piece ofweb into two pieces. Grab tear strength is based on the breakingstrength of the individual threads of the web working in conjunctionwith each other. Grab tear was conducted according to ASTM D1117-01,D5035-95 in two directions: machine direction (MD) and perpendicular tothe machine direction (XD) and is reported in Newton. Results aresummarized in table 3

TABLE 5 Grab tear test of Exemplary and Comparative Bicomponent SpunbondWebs Grab Tear Strength, MD Grab Tear Strength, XD Load/ Load/ Basisbasis basis weight Sample Load Strain weight Load Strain weight (gsm) #(N) (%) (N/gsm) (N) (%) (N/gsm) 50 A-1 42.84 10.94 0.8568 34.44 46.990.6888 B-1 59.6 11.59 1.1920 43.74 25.47 0.8748 C-1 46.84 5.33 0.936851.63 28.44 1.0326 D-1 40.94 8.61 0.8188 33.7 15.04 0.6740 1-1 141.428.73 2.8280 141.4 46.51 2.8280 1-2 141.95 30.6 2.8390 126.78 44.932.5356 100 A-2 84.85 13.92 0.8485 82.14 42.29 0.8214 B-2 80.92 4.030.8092 87.17 16.2 0.8717 C-2 105.63 26.49 1.0563 99.36 17.14 0.9936 D-270.61 13.1 0.7061 95.24 16.55 0.9524 2-1 298.89 35.28 2.9889 297.2 55.012.9720 2-2 413.42 52.06 4.1342 337.51 53.22 3.3751 150 A-3 170.78 19.881.1385 146.16 51.13 0.9744 B-3 95.96 5.33 0.6397 95.61 13.25 0.6374 C-3133.93 13.75 0.8929 143.53 12.67 0.9569 D-3 126.21 25.43 0.8414 110.4824.31 0.7365 3-1 534.25 39.82 3.5617 495.36 52.85 3.3024 3-1 693.5858.03 4.6239 618.28 68.47 4.1219

Table 5 suggests that at a given basis weight, the spunbond webs withPTT in the sheath (Examples 1 and 2) exhibit substantially higher grabstrength both in the machine direction and the cross direction ascompared to the spunbond webs with PTT in the core (Comparative ExamplesB and C) and to 100% pure PTT (Comparative Example D) and 100% pure PET(Comparative Example A). Furthermore, at 100 gsm and 150 gsm, thespunbond webs containing 25 weight % PTT in the sheath (Examples 2-2 and2-3) are stronger than those containing 50 weight % PTT in the sheath(Examples 1-2 and 1-3).

Trapezoidal tear strength, is a measure of ability to resist a continuedtear. The test specimen is trapezoid in shape. A slit is made in thesample for the tear and effort required to continue the tear across theweb is measured. Trapezoidal tear was conducted according to ASTM 5733,and is reported in newton.

TABLE 6 Trapezoidal tear of Exemplary and Comparative BicomponentSpunbond Webs Trapezoidal tear/ Trapezoidal tear, basis weight, [Basisweight Sample MD MD (gsm) # (KPa) (KPa/gsm) 50 A-1 148.93 2.9786 B-199.29 1.9858 C-1 100.67 2.0134 D-1 91.01 1.8202  1-1 267.53 5.3506  2-1260.63 5.2126 100 A-2 319.93 3.1993 B-2 157.21 1.5721 C-2 153.07 1.5307D-2 154.45 1.5445  1-2 479.89 4.7989  2-2 619.17 6.1917 150 A-3 >827.4 —B-3 315.791 2.1053 C-3 199.955 1.3330 D-3 244.083 1.6272  1-3 714.3224.7621  2-3 >827.4 —

Table 6 shows that at a given basis weight, the spunbond webs containing25 weight % PTT in the sheath (Examples 2-1, 2-2, and 2-3) are moreresistant to tear as compared to spunbond webs containing 50 weight %PTT in the sheath (Examples 1-1, 1-2, and 1-3).

1. A nonwoven web comprising a plurality of continuous spunbondedbicomponent fibers, wherein each of the plurality of bicomponent fiberscomprises: a) 75% by weight of poly(ethylene terephthalate) in a core;and b) 25% by weight of poly(trimethylene terephthalate) in a sheathsurrounding the core. wherein the amounts in % by weight are based onthe total weight of the each of the plurality of bicomponent fibers. 2.The nonwoven web of claim 1, wherein the bicomponent fibers have anaverage fiber diameter in the range of 2 microns to 20 microns.
 3. Thenonwoven web of claim 1, wherein the nonwoven web has a basis weight inthe range of 25 gsm to 500 gsm.
 4. The nonwoven web of claim 3, whereinthe nonwoven web has a machine direction and a cross direction and abasis weight in the range of 50 gsm to 150 gsm.
 5. The nonwoven web ofclaim 4, wherein the nonwoven web has a tensile strength per unit basisweight in both the machine direction and the cross direction, measuredaccording to ASTM D1117-01, D5035-95, in the range of 0.75 N/gsm to 5N/gsm.
 6. The nonwoven web of claim 4, wherein the nonwoven web has agrab tear strength per unit basis weight in both the machine directionand the cross direction, measured according to ASTM D1117-01, D5035-95,in the range of 1.5 N/gsm to 10 N/gsm.
 7. The nonwoven web of claim 4,wherein the nonwoven web has a Mullen burst per unit basis weight inboth the machine direction and the cross direction, measured accordingto ASTM D1117-01, D5035-95, in the range of 3.5 KPa/gsm to 10 KPa/gsm.8. The nonwoven web of claim 4, wherein the nonwoven web has atrapezoidal tear strength per unit basis weight in both the machinedirection and the cross direction, measured according to ASTM 5733, inthe range of 0.4 N/gsm to 5 N/gsm.
 10. The nonwoven web of claim 1,wherein the poly(trimethylene terephthalate) is made by polycondensationof 1,3-propanediol derived from a renewable source and terephthalic acidor acid equivalent.
 11. The nonwoven web of claim 1, wherein thepoly(trimethylene terephthalate) contains at least 20% renewably sourcedingredient by weight.
 12. The nonwoven web of claim 1, wherein thenonwoven web has a renewably sourced content of at least 5% by totalweight of the web.
 13. The nonwoven web of claim 1, wherein thepoly(trimethylene terephthalate) comprises titanium dioxide.
 14. Anarticle comprising the nonwoven web of claim
 1. 15. A nonwoven webcomprising a plurality of continuous spunbonded bicomponent fibers,wherein each of the plurality of bicomponent fibers comprises: a) 50% byweight of poly(ethylene terephthalate) in a core; and b) 50% by weightof poly(trimethylene terephthalate) in a sheath surrounding the core,wherein the amounts in % by weight are based on the total weight of thebicomponent fiber.